This application pertains to the art of video control circuitry and more particularly to diagnostic scanners incorporating a video output display. The invention is particularly applicable to ultrasonic diagnostic scanners operating in the B scan mode, i.e., examining a planar region of a patient. Although the invention will be described with particular reference to ultrasonic scanning equipment, it will be appreciated that the invention has other applications such as controlling displays from computerized tomographic scanners and other diagnostic equipment which produce video displays and to broader applications incorporating video control circuitry generally.
Video display devices for diagnostic equipment commonly consist of a patient scanning means for scanning the patient and determining diagnostic values corresponding to small incremental subregions of the patient. Diagnostic values, such as accoustic reflectivity or radiation absorption, are derived by the scanner for each subregion. The diagnostic values derived from each pass of the scanner are stored at a plurality of addresses in a memory--each address corresponding to one subregion. Commonly, scanners make a plurality of passes deriving a plurality of diagnostic values for each of many subregions. The plurality of diagnostic values derived for each subregion are generally summed, averaged or compared for substitution with diagnostic values at each memory address.
After sufficient passes, the diagnostic values at each address are used to create a video display. The position in the display is determined by and corresponds to the position of the subregion in the patient. Mathematical analysis of the values, such as convolutions, Fourier transformations, least-squares analysis, and others, may be employed to adjust the stored diagnostic values to improve the quality of the display. The grey tone at each position in the display is related to the magnitude of the diagnostic value at each address.
A standard video display has about 480 parallel scan lines. In a black and white video monitor, each scan line can be cut into most any number of display positions, commonly, called "pixels". For convenience, each scan line has been commonly cut into 512 pixels. This, in turn, requires 262,144 memory addresses which are commonly gained by using a 512.times.512 memory--a readily purchased electronic commodity.
The display by the nature of video monitors, being a planar rectangular grid of pixels, the subregions of the patient selected are generally chosen to be a planar, rectangular grid of subregions. The rectangular grid is again 512 subregions square.
Oftentimes, a medical diagnostician finds that only a small part of a planar region scanned is of medical interest. Accordingly, the value to the diagnostician of the video display is improved if the smaller region of interest is enlarged for easier viewing. Because the controls for conventional video monitors in diagnostic equipment are generally digital controls, the image commonly can be enlarged only by powers of 2. That is, a diagnostician can view the entire planar region; a quarter of the planar region; an eighth of the planar region, etc.
Conventionally, the controls for video displays for diagnostic scanners use read zoom implementations to enlarge the display size. A read zoom enlarges the display by displaying only a fraction of the diagnostic values stored in the memory but displaying each one a plurality of times. For example, if only a half the memory elements in the X direction and half memory elements in the Y direction are to be displayed the 512.times.512 memory has effectively been reduced to a 256.times.256 memory. However, the 256.times.256 memory is still displayed on a 512.times.512 pixel video display. Thus, each memory element generates four pixels of video display. Even interpolating the diagnostic values in adjacent memory elements only partially improves the picture. Further, enlargements such as eight or sixteen times form a very coarse display. Further, although the display is enlarged, the resolution is not improved because the same data is displayed only larger.
In ultrasonic diagnostic scanners the subregions which diagnostic value represent, is determined with a system such as that shown in the article by Joseph H. Holmes, William Wright, Edward P. Meyer, G. J. Posakony and Douglass H. Howry entitled "Ultrasonic Contact Scanner for Diagnostic Application", The American Journal of Medical Electronics, Vol. 4, No. 4 pp 147-152 October-December, 1965. In such a system, an ultrasonic transducer is moved across the surface of the patient with a rocking motion to view a planar region therebeneath. As the transducer is moved, it transmits ultrasonic accoustic pulses and receives echoes from tissue interfaces in the body. The strength of an echo is an indication of the accoustic reflectivity of a subregion. The position of the subregion is easily determined geometrically from the position of the transducer, the angular orientation of the transducer, and the length of time from transmission of an ultrasonic pulse to the receipt of each echo. The subregions, position of the transducer and angular orientation of the transducer are commonly referenced in terms of an x,y coordinate system. Conventionally, the processing equipment for deriving appropriate address of the memory for each subregion from the position and orientation of the transducer treats the x position, y position, slope of x, and slope of y values each as independent variables. This is a relatively large number of variables to be processed and requires a large amount of processing circuitry.
Traditionally, in ultrasonic scanners the video monitor is oriented so that the scan of the electron beam is vertical. This entails orienting the video display tube 90.degree. rotated from most other video displays. This is done perhaps because the ultrasonic pulses are transmitted through the body often in a vertical direction or at an angle with respect to the vertical. Further the 512.times.512 memory produces a roughly square display or 1.times.1 aspect ratio allowing the top of the screen to be used for displaying textual material such as the patient's name, the date, the scale and other diagnostic information. However, a cross section of the human body is not generally square. Rather, for patients resting on their backs, the cross section is wider than it is high. Thus, the roughly square display is often awkard for displaying planar regions of the human patient.